Reach Mako Storage and Down the Pipe are the first quests in Chapter 7, "A Trap Is Sprung", in Final Fantasy VII Remake, taking place in Mako Reactor 5. After reaching Mako Reactor 5, Cloud Strife, Barret Wallace, and Tifa Lockhart infiltrate the reactor to destroy it.
Walkthrough[]
As Barret obtained the 
Light Machine Gun, this is a good opportunity to upgrade weapons and check equipment. No vending machine is available. If the player has 
Elemental Materia, pairing it with 
Lightning Materia on Tifa Lockhart is useful, as it allows her to deal more damage to the enemies fought here, most of which are weak to lightning damage.
Sliding down the pipe.
When the quest starts, approach the walkway, and Tifa will point out the pipes can be used to descend further. Follow her and Barret in climbing onto the pipe to reach the armory. To the left, three hi-potions can be obtained from a treasure chest, and approaching the door will lead to a path straight into the core. Monodrives will be encountered here, which can be dealt with quickly using physical abilities, although 
Thunder will wipe them out quickly. Proceed down the ladder to the left, and open the treasure chest for two bottles of echo mist and then proceed left down the usual path. Monodrives and Slug-Rays are encountered; the same tactics apply, although Slug-Rays are more durable. Take the ether from the treasure chest and then proceed down the ladder.
On the ladder, use the walkway across, and Sweepers appear along with two Laser Cannons. The Laser Cannons are out of reach of melee attacks, meaning Barret must destroy them while dodging the Sweepers' lunging attacks. Once dealt with, the Sweepers can be defeated with Thunder, or using a character imbued with lightning and elemental materia to pressure them, allowing Tifa to lay into them with Unbridled Strength martial techniques, or Cloud to use Punisher Mode to stagger or destroy them. Once the enemies are destroyed, head down the ladder and open the treasure chest on the end to obtain a bulletproof vest. Take the ladder down to the core and approach.
At the core, a cutscene commences, at which point, proceed to the core and interact with it. This leads to the next quest, "Escape from the Reactor".
Hard mode tips[]
The enemies are significantly more durable and deal more damage than before, and due to the restrictions on MP, conserving it is important. It is best to avoid casting spells at this stage, saving them for the boss later in the chapter. 
Steadfast Block Materia is helpful on Cloud for surviving their attacks while in Punisher Mode to counterattack, and Tifa should use attacks such as Starshower and Focused Strike often to avoid damage. Barret can use Lifesaver with Steelskin, and cast Regen on him for durability.